1. Field of the Invention
The present invention relates to a battery and a method for manufacturing a battery.
2. Description of the Related Art
In recent years, various types of batteries have been proposed as power sources for portable devices and cellular phones and also as power sources for electric and hybrid vehicles. For example, Japanese Patent Application Publication No. 10-269999 (JP-A-10-269999) describes an example of such batteries, which has a power generation element, a case member for accommodating the power generation element therein, and an opening closure member for closing an opening of the case member, and in which the case member and the opening closure member are welded to each other.
The battery described in JP-A-10-269999 has a box shape, and has a main body case (case member) which is a rectangular parallelepiped in external shape and which includes a bottom and four sides which form edges of the opening, and a lid member (opening closure member) which is rectangular in external shape. The lid member has thin edges around its periphery, and a projection projecting in the thickness direction at its center. The box-shaped battery is assembled by first installing a battery element (power generation element) inside the main body case, inserting the projection of the lid member into the main body case, and causing the thin edges of the lid member to contact the upper ends of the respective sides of the main body case to close the main body case. The main body case and the lid member are secured to each other by welding the thin edges of the lid member and the upper ends of the respective sides of the main body case from above the box-shaped battery.
In such batteries, the case member is closed by the opening closure member with a portion (case inside part) of the opening closure member positioned internally of the sides of the case member. However, if the outer dimensions of the case member and the opening closure member are varied, the case member and the opening closure member may rub against each other while inserting the case inside part of the opening closure member into a space internally of the sides of the case member. This may generate foreign matter such as metal powder. Thus, the outer dimensions of the case inside part are made small relative to the internal dimensions of the sides of the case member in consideration of the dimensional tolerances of the case member and the opening closure member, in order that the case inside part can be easily inserted into the case member. As a result, there is formed some gap between the sides and the case inside part in the case member.
The sides of the case member, especially the sides forming longer edges of the opening, are occasionally deformed toward the inside (warped inwardly) of the case member when it is molded. In the case where a gap is allowed between the sides and the case inside part as discussed above, however, such warping deformation of the sides of the case member causes the opening edges formed by the sides to be also warped inwardly. This causes the gap between the case inside part of the opening closure member and such warped sides to be inconstant as seen in the direction along the opening edges. In addition, in welding them to each other along the opening edges, the welding position is varied in the direction of the thickness of the sides. Thus, the sealing strength may be locally lowered. Meanwhile, the tolerances in outer dimensions of the case member and the opening closure member may be reduced. In such a case, however, the case inside part and the sides may rub against each other while positioning the case inside part inside the case member, which may generate foreign matter such as metal powder inside the case member and may cause deterioration in performance of the battery or short circuiting.